1. Technical Field
The present invention relates generally to a voice over Internet protocol (VoIP) system, and in particular, to a voice over Internet protocol system that assigns addresses through network address translation.
2. Related Art
Voice over Internet protocol (VoIP) is a novel communications service that provides a voice call not over the public switched telephone network (PSTN) but over the Internet. Due to the use of a packet-based network, domestic/international calls can be made free of charge by deploying voice over Internet protocol. Voice over Internet protocol can even deliver video information as well as audio information using the ITU-T H.323 protocol.
A voice over Internet protocol (VoIP) system includes the Internet as a backbone. Gateways and personal computers (PCs) are connected to the Internet. The gateways are connected to public switched telephone networks that are in turn connected to telephones. The telephones and the personal computers are endpoints that are capable of carrying out communications by voice (mandatory), moving pictures (optional), and data (optional) in one-to-one communications or video conferencing. These terminals can carry out real-time bi-directional communications with the gateways or other terminals. The gateways enable real-time bi-directional communications between terminals (e.g., personal computers) connected to the Internet (that is, the packet-based network) and terminals (e.g., telephones) connected to the public switched telephone networks or an integrated services digital network (ISDN).
The voice over Internet protocol system must use a unique Internet protocol (IP) address to communicate over the Internet. However, permanent assignment of unique Internet protocol addresses for connection to the global Internet results in a shortage of available unique Internet protocol addresses.
To solve the above problem, network address translation (NAT) is used. Network address translation is a technology which allows all of the hosts on a private network to access the Internet via a single public Internet protocol address by translating a plurality of temporary inside addresses to the public Internet protocol address. The resulting avoidance of collisions with outside Internet protocol addresses enables use of more inside Internet protocol addresses than regulated.
In such a network, transmission control protocol/Internet protocol (TCP/IP)-based data coexists with voice over Internet protocol (VoIP)-based voice. Despite use of the same transmission control protocol/internet protocol network layer, network address translation does not support existing protocols used for general data for the voice over Internet protocol. Moreover, most networks provide control only to general data internally, and exclude voice data. Since the voice over Internet protocol system can access the Internet by a unique Internet protocol address only, as compared to general private network systems, Internet protocol efficiency of the voice over Internet protocol system is low.
The following patents are considered to be generally pertinent to the present invention but are burdened by the disadvantages set forth above: U.S. Patent Publication No. 2001/0043571A1 to Jang et al., entitled MULTIPLE SUBSCRIBER VIDEOCONFERENCING SYSTEM, published on Nov. 22, 2001; U.S. Patent Publication No. 2001/0004361 A1 to Kobayashi, entitled TELEPHONE CONTROLLER FOR VOIP, published on Jun. 21, 2001; and U.S. Patent Publication No. 2001/0030950 A1 to Chen et al., entitled BROADBAND COMMUNICATIONS ACCESS DEVICE, published on Oct. 18, 2001.